Purification of metals and alloys



Patented Dec. 22, 1931 UNITED STATES ALBERT H AI N'AK, OF PHILADELPHIA, PENNSYLVANIA.

PURIFICATION OF METALS AN D ALLOYS No Drawing.

This invention relates to the prification of non-ferrous metals and alloysin general and more specifically to the purification of copper alloys, like brasses, bronzes and kindred alloys.

The principal object of the invention is the elimination of any sulphur which may be present in an impure copper or copper alloy. Another object of the invention is the elimination of certain other impurities which may be present in form of dissolved sulphides in an lmpure copper or copper allo In accomplishing these ob ects, the workability, of the chemical and physical prop erties and the appearance of said metals or alloys, are much improved and thereby their industrial or artistic usefulness is greatly enhanced. v

Sulphur is universally reco ized as being a very undesirable and harm ul impurity in copper and all its alloys. On account of its deleterious properties upon brasses, bronzes and similar alloys, the most exacting precau tions are necessary to avoid their contamination by surp'hur during their preparation or fabrication. Practically all specifications limit the sulphur content to very. small amounts, usually to no more than a few hundredths of one per-cent. If it is present in the aforementioned metals or alloys in rela tively larger amounts, it renders them wholly 1 unfit for use in the foundry, rolling mill or workshop..

Iron, aluminum, arsenic, antimony, silicon and oxygen are those elements which are also considered as being undesirable impurities in the above metals or alloys with the exception of certain special cases when some of as a rule, in substantial quantities. Ordinarily, they are also limited to very small percentages.

Copper and its alloys take up sulphur with great avidity from any available source whatlarge scale industrial operations.

these elements are purposefully added and' Appfication filed January 19, 1931. Serial No. 509,890.

soever and as a matter of fact, it is rather diflicult to prepare them free of sulphur in Sulphur is a very widely distributed element and it is present in the metals fromwhichthe alloys are 5 prepared, also in the fuels which ordinarily are used for melting them and in the fluxes and tools they oftentimes come in contact with. Alloys carefully prepared from virgin metals seldom, if ever, contain suflicient sulphur-to render them useless, but whenever and wherever scrap metals, industrial waste, byproducts and residues are utilized either wholly or partly for the manufacture of the above metals and alloys, the sulphur almost 00 always contaminates the product and this oftentime is so serious, that the metals or alloys either have to be mixed with suflicient sulphur-free metals or alloys to render them at least serviceable, or else they have to be 55 diverted from their intended use, both of which procedures mean, of course, added cost. However, even if the sulphur content .of said metals or alloys is sufliciently low to be within a specified maximum, an almost complete removal of it very substantially improves the metals or alloys from point of workability as-well as from point of chemical and physical properties and appearance. The utilization of scrap metals, metallic byproducts and residues. from the production of so-called nonferrous ingot metals or alloys is the foundation of a substantial industry and it is primarily there where the value of this invention becomes apparent. r Up to the present time, no. method was known to remove the sulphur from said metals or alloys without virtually removing all other constituents but copper and. certainly no method was known which, besides' accomplishing the above, simultaneously removes br lowers such undesirable impurities as'are present'in form of sulphides in the metals or alloys and leaves same in a properly' deoxidized condition. It is generally accepted that with'the exception of manganese, of all the metals, copper has the greates aflinity for sulphun The other metals usually composing a copper alloy also have marked aflinities for sulphur but weaker than copper. On the other hand, of all the metals ordinarily composing a copper alloy, the copper has the least afiinity for oxygen. The oxidation of the sulphur to sulphur dioxide and the expulsion of the latter by poling, is the present method of removing it from an impure copper. In this procedure, large amounts of copper are oxidized and subsequently slagged, as well as the refractories of the furnaces are rapidly destroyed by the combined action'of mechanical agitation and chemical corrosion at elevated temperatures. Generally speaking, a similar process is used to remove various impurities from copper alloys and its principle is progressive oxidation. The constituents are oxdized in proportion to their aflinity for oxygen and if it is carried sufliciently far enough, all the constituents but copper will be oxidized, although substantial portions of the latter will also be oxidized. The sulphur, however, is not removed by even such a radical process excepting only small fractions of it. Until the point of almost pure copper is reached, the sulphur will remain in the metal or alloy. Therefore, by the processes generally practiced at the present time, the removal of the sulphur from a copper alloy. is impossible.

I have discovered that the alkali or alkali earth metals have the property of uniting with the sulphides of the metals ordinarily composing a copper alloy. In this manner,

complex sulphides are formed which are also soluble in the metals or alloys. It'does not appear that such complex sulphides form by replacement of the metallic radicals in the sulphides by the alkali or alkali earth metals, but rather it seems that they form bysimple addition. Ive also discovered that these complex sulphides much more readily dissolve in molten alkalies if strongly reducing conditions are maintained, than in metals or alloys, and ,thus they can be completely extracted from said metals or alloys. By virtue ofth'e great difierence between the specific gravity of a molten alkali and that of a molten metal or alloy, an easy separation of the two is evident.

l have, furthermore, discovered that the sulphur which is contained in an alloy of copper like brass, bronze, German silver, etc., is not distributed among the components of such an alloy according to their respective afiinities. The sulphur which is contained in arr impure copper alloy, united proportionally much more to iron, arsenic, antimony, etc., if they are also present, or to tin and lead, than tocopper, in spite of the fact aaeaeaa that copper has the greatest aflinity for sulphur. This is possibly explained by the fact that in an alloy, the copper being in chemical combination with some of the constituents like zinc or tin, for instance, does not behave like elemental copper.

From the foregoing, it is apparent that it is not sulphur per se which is removed by my invention, but the sulphides of all the metals which existed in solution in the metal or alloy. The union of sulphur with the various elements such as copper, tin, lead, zinc, arsenic, antimony, iron, aluminum, silicon, etc., remains unbroken, only they are rendered much more soluble in a superimposed Inolten alkali than they are in the molten metal or alloy and thus they are separated. Dissolving the alkali in water discloses that only traces of alkali sulphides are present and that the metallic sulphides are in such proportions which bear no relationship to chemical affinities whatsoever. Inasmuch as substantial portions of such impurities as iron, aluminum, arsenic, antimony and silicon are united with sulphur, it is also evident that theyll be removed or lowered by the application of my invention. The alkali or alkali earth metals are recognized as the most powerful reducing agents known, thus if any oxygen is present in the alloys, it also will be removed or lowered by the application of my invention.

The application of the invention is simple and cheap. Sodium is the alkali metal and sodium carbonate is the alkali preferably used on account of their cheapness and easy handling. The sodium carbonate is first melted on top of the molten copper or copper alloy which'is held in a furnace or some other suitable vessel and is maintained under strong reducing conditions. This can be attained by graphite or some other preferably crystalline form of carbon. The sodium is then introduced into the metal by means of some device which forces it under "the metal such as the so-called phosphorizers are. The quantity of the alkali'andthe alkali metal, .of course, depends upon the amount of sulphur present which has to be determined by chemical analysis. The reaction isinstantaneous and in a few minutes, the sulphides are extracted by the molten sodium carbonate which then can be skiinmed 01f. Contacting the molten alkali holding'the sulphides in solution with the underlying metal for any length of time, does not cause the sulphides to be reabsorbed by the metal or alloy provided the reducing conditions are maintained. Concentration of the sulphides in the metal and in the melt has also no noticeable influence upon the outcome and the process is applicable at very small and at verygreat concentrations.

As a specific example of my invention, 20,000 pounds of an alloy have the following chemical composition and having the following physical properties:

Yield point 20,000 lbs. per sq. inch Ultimate strength 33,000 lbs. per sq. inch Elongation 17.5% in 2 inches Reduction of area and castings made from same according to standard practice in green sand molds exhibited numerous blowholes, spongyness and a dark colored and spotty surface, also a marked tendency to bite into the sand, was treated as described with 60 lbs. of sodium and 400 lbs. of sodium carbonate and obtained 19,900 lbs. of an alloy having the foland having the following physical properties:

Yield point Ultimate strength Elongation Reduction of area Brinell hardness 385a 29,000 lbs. per sq. inch 43,000 lbs. per sq. inch 375% in 2 inches and castings made from same exhibited a dense structure, freedom from blowholes and bright color free from spots and a smooth surface such as alloys prepared with care-from virgin metals would yield. Also obtained 612 pounds of the carbonate meltwhich contained:

Cu 2.50% Sn 1.70 Pb 1.25 Zn 1.00 Fe 3.15 Ni .50 As .30 Sb 3.20 S 3.72

besides Na, CO SiO A1 0 and MgO, percentages of which were not determined.

The alloy having been treated as described was prepared wholly from scrap metals and residues containing the constituents of the alloy and received before the treatment as thorough a metallurgical refining as present practice permits. The latter consisted in an oxidizing'blow with air in presence of alkaline fluxes, followed by a reduction with carbonaceous matter. Such an alloy with eventual slight modifications is a rather typical alloy made from secondary sources. It is rarely that such alloys contain less than 05% sulphur and it is often that they contain more than 10% which, with the exception of certain leaded alloys, is above the maximumlimit allowable for copper alloys' As it is apparent from the chemical analy-.

sis of the treated alloy, took place by the application of the invention and in consequence of this, the alloy was greatly improved.

claim:

1. The process of removing sulphur from impure metals or metallic alloys which comprises treating said metals or metallic alloys in the molten state with sodium, in presence of amolten layer of sodium carbonate.

2. The process of purifying impure copper or copper alloy which comprises treating said copper or copper alloy in themolten state with a metal of the group comprising alkali and alkali earth metals and contacting at the same time said copper or copper alloy with a layer of a molten alkali under reducing conditions.

p 3. The process of purifying impure copper or copper alloy which comprises treating said copper or copper alloy in the molten state a radical purification with sodium and contactingat the same time I said copper or copper alloy with a layer of molten sodium carbona e under reducing conditions.

4. The process of removing sulphur from impure copper or copper alloy whichcomprises treating said copper or copper alloy containing the compounds of'sulphur, from the copper or copper alloy.

5. The process of removing sulphur from impure copper or copper alloy WhlCh comprises treating said copper or copper alloyin the molten state with sodium while maintaining a layer of molten sodium carbonate on sand copper or copper alloy under reducing conditions and then separating the molten sodium carbonate containing the compounds of sulphur fromthe molten copper or copper alloy.

ALBERT HANAK. 

